Ignition system with series connected transistor and common core inductors to speed switching



Feb. 28, 1967 R c. MOLAUGHLIN IGNITION SYSTEM WI TH SERIES CONNECTED TRANSISTOR AND COMMON CORE INDUCTORS TO SPEED SWITCHING Filed April 2, 1964 WHIEIEIEFM- I NVE NTOR.

Roberf C McLaughlin Y W6 ATTYSd Illinois Filed Apr. 2, 1964, Ser. No. 356,830 3 Claims. (Cl. 315-219) This invention relates to ignition systems for internal combustion engines, and more particularly to a transistorized ignition system employing a plurality of switching transistors.

With the increased commercial availability of transistors, transistorized ignition systems for use in connection with vehicular internal combustion engines have become increasingly prevalent. One difiiculty with such systems is that the high reverse voltage spike occurring in the ignition coil can cause damage to the output transistor or transistors unless the transistors reverse breakdown capabilities are extremely high. Such transistors may be expensive and difiicult to obtain.

It has been proposed to connect a pair of switching transistors in series with the ignition coil and to provide circuitry such that the two transistors cooperate to resist the high reverse voltages. In addition, the reverse voltage breakdown capabilities of a transistor may be improved by applying reverse bias thereto when the transistor is cut off by means of an inductance coil. Such reverse bias also increases switching speed to improve voltage output. When two or more transistors are used in series and are controlled by inductance coils, however, difficulties may arise in obtaining simultaneous cut ofi of the transistors.

Accordingly, it is an object of this invention to provide an improved transiston'zed ignition system.

Another object of the invention is to provide a transistorized ignition system wherein a plurality of transistors are connected in series and wherein the transistors are reverse biased simultaneously when switching off.

A feature of the invention is the provision of a plurality of switching transistors connected in series with the ignition coil in an ignition system, and the further provision of a control circuit including a plurality of inductance coils for respectively reverse biasing the transistors, which inductance coils are coupled through a common core.

Another feature of the invention is the provision, in an ignition system having a plurality of switching transistors connected in series, of an inductance coil connected across the emitter and base portions of each of the switching transistors, with all of the inductance coils having a common core.

In the drawing, there is shown a schematic diagram of a transistor ignition system for an internal combustion engine constructed in accordace with the invention.

In practicing the invention, a pair of switching transistors have their emitter to collector paths connected in series with the ignition coil across a voltage source. A control circuit for switching the transistors is energizable by the closing of intermittently operable breaker points, or other means. The control circuit includes resistors 31 and 32 with diode 33 to forward bias the transistors into conduction, and further includes a pair of inductance coils connected across the base to emitter portions of the respective transistors. The induction coils are wound on a common core to provide coupling therebetween for simultaneous switching of the transistors.

Referring now more particularly to the drawing, there is shown a circuit extending from storage battery 11 through an ignition switch 12 and a ballast resistor 13 to the emitter electrode 14 of transistor 15. The collector electrode 16 of transistor 15 is connected to the United States Patent 3,3@7,973 Patented Feb. 28, 1967 emitter electrode 17 of transistor 18. The collector electrode 19 of transistor 18 is connected to the primary winding 21 of ignition coil 22 to complete the circuit from the battery. The secondary winding 23 of ignition coil 22 is connected to a distributor which provides high voltage firing pulses to the internal combustion engine as is well known in the art.

In order to produce high voltage pulses in the secondary winding 23 of ignition coil 22, transistors 15 and 18 must be switched off to interrupt the current in primary Winding 21. This switching is governed by a control circuit which is energizable and de-energizable by the closing and opening, respectively, of a pair of breaker points 24 which are operable in timed relation with the internal combustion engine.

The control circuit includes a resistor 26 connected across the emitter 14 and base 27 of transistor 15, and a resistor 28 connected across emitter 17 and base 29 of transistor 18. Resistors 31 and 32 provide forward bias for transistors 15 and 18 respectively, when current is passed therethrough. Base 27 of transistor 15 is connected to the breaker points 24 through a resistor 31, and the base 29 of transistor 18 is connected to breaker points 24 through a resistor 32 and a diode 33.

As may be seen, when breaker points 24 open, current through resistors 31 and 32 will be interrupted, removing forward bias from transistors 15 and 18, rendering them nonconductive. This results in a collapse of current in the high voltage coil 22, and a high voltage firing pulse is produced in the secondary winding 23 thereof. As a result of the collapsing field, a high reverse voltage spike is induced in primary winding 21 of ignition coil 22. Zener diode 34 is added in the system as shown to provide protection for transistors 15 and 18 from the high voltage reverse spike. Resistors 36 and 37 divide the voltage equally across each transistor. This allows the use of only one Zener diode instead of one across each transistor as is usually found in such circuits.

In order that a sufiiciently high voltage spike is induced in secondary winding 23 to provide the necessary firing voltage, it is desirable that transistor 15 and 18 be cut off rapidly. In addition, because of the high voltage in secondary winding 23 there is high voltage in primary winding 21 as well, and it is necessary that transistors 15 and 18 be capable of withstanding high reverse voltages. Both of these objectives may be accomplished by reverse biasing the transistors to cut them 011. To do this, induction coils 38 and 39 are connected in parallel with resistors 26 and 28, respectively, across the base and emitter portions of transistors 15 and 18. When breaker points 24 open, the collapsing field in coils 38 and 39 will place a reverse bias on transistors 15 and 18 as desired. Resistors 26 and 28 lower this reverse bias to safe levels and spread it out over a period of time. This insures that transistors 15 and 18 will be reverse biased throughout the reverse voltage applied from primary winding 21.

As may be seen, inductance coils 38 and 39 are wound on a common core. If this were not so, switching of transistors 15 and 18 would not necessarily take place simultaneously. Accordingly, the transistors might work against each other to defeat the objective, that is, a sudden cut off of the current flow through winding 21 of coil 22. However, since the inductance coils 38 and 39 are on a common core, the field thereof will collapse together so that the coils will simultaneously reverse bias transistors 15 and 18. Accordingly, a clear sharp cut oil. occurs and a very high voltage output pulse results.

The use of inexpensive transistors is possible in such a system because of the superior pulsing characteristics which are provided, allowing the transistors to attain much higher reverse breakdown capabilities and providing a much shorter rise time of the output pulse. In addition, it might be possible for some applications, with transistors of a sufiiciently high voltage rating, to utilize the system of the invention in connection with a standard ignition coil, that is, a coil such as is used in a system wherein the current through the coil is broken directly by the breaker points. Such systems generally utilize coils of approximately 100 to 1 winding ratios, which may require a 250-300 volt input pulse to attain the desired output. A system in accordance with the present invention, incorporating the proper type of transistors, would provide a very convenient way for consumers to modify an existing ignition system at a minimum of expense.

It may therefore be seen that the invention provides an improved transistorized ignition system which utilizes a plurality of switching transistors in series with the ignition coil, which transistors are simultaneously cut oil and simultaneously reverse biased to provide a superior pulse to the ignition coil.

I claim:

1. An ignition system for an internal combustion engine used with a vehicular electrical system incorporating an ignition coil, a voltage source, and a pair of intermittently opened breaker points operable in timed relation with the internal combustion engine, said ignition system including in combination, a plurality of switching transistors each having an output, a common and a control electrode, means connecting said common and output electrodes of said transistors in series with each other and with the ignition coil across the voltage source, and control circuit means connected to said control electrodes of said switching transistors for controlling the conductivity of said transistors, said control circuit including a plurality of inductance coils having a common core and being individually coupled between said common and control electrodes of respective ones of said plurality of switching transistors, said control circuit means having additional means connected to the breaker points and being intermittently energized in response to the operation of the breaker points for rendering said transistors conductive and non-conductive, with said inductance coils applying reverse bias to said switching transistors upon deenergization of said control circuit to speed switching of said transistors and to increase the reverse voltage breakdown capabilities thereof, said common core coupling said coils and causing said transistors to switch substantially simultaneously.

2. An ignition system for an internal combustion engine used with a vehicular electrical system incorporating an ignition coil, a voltage source, and a pair of intermittently openable breaker points operable in timed relation with the internal combustion engine, said ignition system including in combination, first and second switching transistors each having base, emitter and collector portions with the emitter to collector paths thereof connected in series with the ignition coil across the voltage source, control circuit means including resistance means connected across the base and emitter portions of said first and second transistors respectively and being energizable in response to the operation of the breaker points for biasing said transistors into conduction, said control circuit means further including first and second inductance coils connected across the base and emitter portions respectively of said first and second transistors and in parallel with said resistance means and applying reverse bias across the base and emitter portions of said first and second transistors upon de-energization of said control circuit means to speed switching of said transistors and to increase the reverse voltage breakdown capabilities thereof, said first and second inductance coils having a common core coupling said coils and causing said transistors to switch substantially simultaneously.

3. An ignition system for an internal combustion engine, including in combination, a voltage source, an ignition coil, first and second switching transistors having base, emitter and collector portions with the emitter to collector paths thereof connected in series with said ignition coil across said voltage source, first and second resistors respectively connected across the base and emitter portions of said first and second transistors, a pair of intermittently openable breaker points operable in timed relation with the internal combustion engine, one of said breaker points being grounded, third and fourth resistors respectively connecting the base portions of said first and second transistors to the other of said breaker points, and first and second inductance coils connected across the base and emitter portions of said first and second transistors respectively and in parallel with said first and second resistors, said first and second inductance coils applying reverse bias to said first and second transistors respectively upon opening of said breaker points to speed switching of said transistors and to increase the reverse voltage breakdown capabilities thereof, said first and second inductance coils having a common core coupling said coils and causing said transistors to switch substantially simultaneously.

References Cited by the Examiner UNITED STATES PATENTS 3,218,512 11/1965 Quinn 3l5209 OTHER REFERENCES C. E. Ruoff, Operation Pickup appearing in Popular Electronics, June 1963, pages 3338, 86.

JOHN W. HUCKERT, Primary Examiner.

D. O. KRAFT, Assistant Examiner. 

1. AN IGNITION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE USED WITH A VEHICULAR ELECTRICAL SYSTEM INCORPORATING AN IGNITION COIL, A VOLTAGE SOURCE, AND A PAIR OF INTERMITTENTLY OPENED BREAKER POINTS OPERABLE IN TIMED RELATION WITH THE INTERNAL COMBUSTION ENGINE, SAID IGNITION SYSTEM INCLUDING IN COMBINATION, A PLURALITY OF SWITCHING TRANSISTORS EACH HAVING AN OUTPUT, A COMMON AND A CONTROL ELECTRODE, MEANS CONNECTING SAID COMMON AND OUTPUT ELECTRODES OF SAID TRANSISTORS IN SERIES WITH EACH OTHER AND WITH THE IGNITION COIL ACROSS THE VOLTAGE SOURCE, AND CONTROL CIRCUIT MEANS CONNECTED TO SAID CONTROL ELECTRODES OF SAID SWITCHING TRANSISTORS FOR CONTROLLING THE CONDUCTIVITY OF SAID TRANSISTORS, SAID CONTROL CIRCUIT INCLUDING A PLURALITY OF INDUCTANCE COILS HAVING A COMMON CORE AND BEING INDIVIDUALLY COUPLED BETWEEN SAID COMMON AND CONTROL ELECTRODES OF RESPECTIVE ONES OF SAID PLURALITY OF SWITCHING TRANSISTORS, SAID CONTROL CIRCUIT MEANS HAVING ADDITIONAL MEANS CONNECTED TO THE BREAKER POINTS AND BEING INTERMITTENTLY ENERGIZED IN RESPONSE TO THE OPERATION OF THE BREAKER POINTS FOR RENDERING SAID TRANSISTORS CONDUCTIVE AND NON-CONDUCTIVE, WITH SAID INDUCTANCE COILS APPLYING REVERSE BIAS TO SAID SWITCHING TRANSISTORS UPON DEENERGIZATION OF SAID CONTROL CIRCUIT TO SPEED SWITCHING OF SAID TRANSISTORS AND TO INCREASE THE REVERSE VOLTAGE BREAKDOWN CAPABILITIES THEREOF, SAID COMMON CORE COUPLING SAID COILS AND CAUSING SAID TRANSISTORS TO SWITCH SUBSTANTIALLY SIMULTANEOUSLY. 